Forward light scatter and contrast sensitivity in keratoconic patients

Purpose: To compare intraocular forward light scatter in keratoconus patients and controlsubjects and to explore possible relationships with contrast sensitivity. Method: We assessed intraocular straylight in the right eye of 10 visually-normal subjects (34 ± 9 years) and 5 keratoconus patients (31 ± 5 years) using the van den Berg straylightmeter. We also measured contrast sensitivity in both groups, with and without a glare sourceprovided by the Brightness Acuity Tester (BAT) (Marco Ophthalmic Inc. Jacksonville, FL, US),using a Pelli-Robson chart (Sussex Vision International Ltd, West Sussex, UK). Inclusion criteria for the keratoconic patients were chosen to avoid natural causes of increased scatter and to limit the influence of factors that could influence the straylight measurements. Results: Intraocular light scatter was significantly greater in the keratoconic patients than in normal subjects for each eccentricity tested (p <0.027). Baseline Pelli-Robson contrast sensitivity was also found to be lower in the keratoconus group than in the normal subjects.Under glare conditions contrast loss was significantly greater in the keratoconic patients thanin the normal subjects (p <0.023). High levels of negative correlation were found between the magnitudes of intraocular straylight and baseline contrast sensitivity in the keratoconus group. Conclusions: The high values of straylight measured in the keratoconic patients cannot be explained by age or corneal scarring and could be related to the structural degradation of the cornea. Further investigation of intraocular scatter in keratoconus is warranted to improve our current understanding of the visual deficits associated with this disease.